Shuriken are a regular part of morning bukiwaza at Saito Hitohiro Soke's dojo.
One hour of ken or jo and a few minutes of shuriken "suburi" then 30 minutes of shuriken. I had my first shuriken practice today in months -- just started going back to morning keiko... it's so easy to get out of practice with shuriken!
As to 'why' -- the style of shuriken Hitohiro Sensei practices has a throwing motion very similar to 1st ken suburi strike and we concentrate on putting hips into the movement and controlling the strike -- cutting straight down the center.